[alffie]

Baz
Hes screwing you! You only need to use credits if you change the tune, if the previous tuner had "locked" the ECU. To just read codes and stuff you dont need credits. Once the tuner has applied credits to your ECU he doesnt need to anymore. He will "lock" your ECU so only HE can access your ECU without credits, so everytime you change tuners they will need to apply credits to "unlock" the ECU so they can change things.
To go back to the same tuner you should only be paying for Labour not credits.
Justin (double dip) is the best guy I have found for the GM ECUs, Hes the only one that I found that could easily set up stand alone ECUs.